The present invention relates to a picture synthesizing apparatus for synthesizing two or more kinds of video signals to thereby allow a composite picture to be displayed on a monitor device in such a manner that a main picture (or parent picture) is inlaid as a part thereof with a subsidiary picture (or daughter picture) in a compressed form.
With the remarkable advance of semiconductor technology in recent years, digital signal processing techniques employing digital memories tend increasingly to be adopted in various video equipment and apparatus for home use. As an example of such applications, there is known a digital television receiver imparted with a so-called picture-in-picture function (also referred to as P-in-P function in abbreviation) in which two kinds of video signals are synthesized such that a main picture displayed on a monitor device is inlaid with a subsidiary picture in a compressed or contracted form so that two pictures can be simultaneously displayed. The technology concerning this picture-in-picture function is discussed, for example, in Japanese periodicals titled "Television Technology", No. 9 (Sept., 1984), p.p. 25-29, and No. 12 (Dec., 1984), p.p. 31-", Japanese Patent Laid-Open No. 92015/1979 (JP-A-54-92015) and others.
The above-mentioned picture-in-picture function known heretofore was developed for application to the television receiver. By virtue of this picture-in-picture function, a picture originating in a television broadcast, a video tape recorder (VTR) or the like is displaced as a parent or main picture available from another source, such as another VTR, a video disc system, satellite broadcast or the like, is simultaneously displayed as a subsidiary picture (daughter picture) as a part of the main picture. In most of the picture-in-picture type television receivers, the P-in-P function is provided by controlling the driving signals of the cathode ray tube of the television receiver such that the video signal for the main picture is changed over to the video signal for the subsidiary picture at a predetermined local area of the main picture. (This can be accomplished in general by storing the video signal for the subsidiary picture in a video memory and reading therefrom the same video signal in timing with synchronization for the main picture so that the subsidiary picture can be inlaid in the main picture).
In this connection, it is noted that the amplitude levels of the video signals as inputted are not always constant. By way of example, at the present state of the television technology, there may occur as large a deviation or fluctuation as 1.+-.0.2 V in the amplitude level among the receiver channels at the stage of tuner. Needless to say, such variation in the amplitude level brings about a significant difference in contrast between the main picture and the subsidiary picture to the discomfort of the viewer. Particularly in case the main picture is bright while the subsidiary picture is dim, the latter becomes more difficult to view. Further, since the synthesized signal is subjected to processing in the monitor apparatus, variation in the amplitude level of both or either one of the video signals for the main and subsidiary pictures will result in the appearance of buzz noise and white eyesores as well as very poor contrast, particularly when the pictures are dim, to great disadvantages. Unless the video signals to be synthesized for the main picture and the subsidiary picture coincide with each other in respect to the chrominance signal level, a difference in color density will occur between the main picture and the subsidiary picture, giving rise to unnaturalness. As an attempt to solve this problem, it is known heretofore to perform an automatic color control processing (also referred to a ACC processing) on the composite video signal for the main picture. In that case, in order to accomplish the alignment of the chrominance signal level for the main picture and the subsidiary picture, it is possible to perform processing such as luminance/chrominance signal separation (also referred to as Y/C separation), modulation/demodulation and the like on both of the composite video signals for the main picture and the subsidiary picture. In this connection, it is observed that the Y/C separation mentioned above is usually accompanied with degradation in the frequency characteristic particularly for the luminance or Y signal), because each of the luminance (Y) signal and the chrominance (C) signal for the main picture requires the whole frequency band, differing from the case of the Y/C signals for the subsidiary picture. To prevent deterioration in the frequency characteristics upon Y/C separation, a comb line filter, implemented by making use of a 1H-delay line or the like, it is necessitated, which means, however, that the circuit scale is undesirably increased.
It is therefore a general object of the present invention to provide a picture synthesizing apparatus which allows a main (parent) picture and a subsidiary picture (daughter picture) to be displayed in a satisfactory way.
It is a specific object of the present invention to provide a picture synthesizing apparatus which allows both a main picture and a subsidiary picture to be displayed at the preferred brightness.
Another specific object of the present invention is to provide a picture synthesizing apparatus capable of displaying a synthesized or combined picture in which coloration of both the main picture and the subsidiary picture can be maintained constant steadily.
Still another specific object of the present invention is to provide a picture synthesizing apparatus which can be implemented in a small scale circuit configuration and which can nevertheless maintain the coloration of a main picture and a subsidiary picture at a predetermined ratio.
A still further specific object of the present invention is to provide a picture synthesizing apparatus in which degradation and deterioration in the frequency bands of composite video signals for the main picture and the subsidiary picture as well as image quality thereof can be suppressed to minimum.